Optimizing molecules for photonic use could provide a foundation for low-power, high-speed, all-optical signal processing. Researchers at the Georgia Institute of Technology are working to create these molecules for a variety of uses, including medical imaging.

All-optical switching and processing enables speedy transmission of data, eliminating the need to convert photonic signals to electronic signals, and back again. Existing electrooptical technology may ultimately be able to provide transmission speeds of up to 100 Gb/sec. However, all-optical processing could theoretically transmit data at speeds as high as 2000 Gb/sec.

“This work provides proof that at least from a molecular point of view, we can identify and produce materials that have the right properties for all-optical processing,” says Seth Marder, a professor in the Georgia Tech School of Chemistry and Biochemistry and coauthor of the paper. “This opens the door for looking at this issue in an entirely different way.”

To make all-optical processing even feasible, the team had to develop high-performing materials (optimized molecules). The polymethine organic dye materials created by Georgia Tech combine large nonlinear properties, low nonlinear optical losses, and low linear losses. But the optical properties have only been demonstrated in solution. The next step is to put them together so that they exhibit high density and useful physical forms that are stable under operation. For the materials to have practical value, the researchers must incorporate them in a solid phase for use in optical waveguides, along with other challenges.

Marder and collaborators in Georgia Tech’s Center for Organic Photonics and Electronics (COPE) have been working on the molecules for several years, refining their properties and adding atoms to maximize their length without inducing symmetry breaking (unequal charges building up within molecules). This molecular design builds on earlier research with smaller molecules. Both experimental work and theoretical studies have been done.

“Even if the frequency of signals coming and going is high, there is a latency that causes a bottleneck for the signals until the modulation and switching are done,” says Joseph Perry, coauthor and professor in the school of chemistry and biochemistry. “If we can do that all optically, then that delay can be reduced. We need to get electronics out of the system.”

The design strategies could be applied to the development of even more active molecules. And Marder believes the existing materials could be modified to meet the needs of all-optical processing.

Perry and Marder emphasize that many years of research remain ahead before the materials are practical. But they believe the approach they’ve developed leads toward all-optical systems.

“While we have not made all-optical switches, what we have done is provide a fundamental understanding of what the systems are that could have the combined set of properties that would make this possible,” Marder says. “Conceptually, we have probably made it over the hump with this class of molecules. The next part of this work will be difficult, but it will not require a fundamental new understanding of the molecular structure.”

Details of these materials were reported in Science Express, the rapid online publication of the journal Science. The research was funded by the National Science Foundation (NSF), the Defense Advanced Research Projects Agency (DARPA) and the Office of Naval Research (ONR).